The conventional devices for dispensing the toilet bowl cleaning agent are capable of discharging a certain amount of the cleaning agent into the water tank of a flush toilet after each flushing. The conventional devices are generally deficient in design in that the strength of the toilet bowl cleaning agent in the water contained in the water tank of the flush toilet is not kept constant from flush to flush. In other words, the toilet bowl cleaning agent is made denser under the circumstances that the flushing is done at brief intervals. On the other hand, the strength of the cleaning agent tends to be excessive if the flushing is done only once in a while. To sum up, the conventional devices for dispensing the toilet bowl cleaning agent are not efficient.